1. Field of the Invention
The present invention relates to a relay device and, more particularly, to a radio frequency (RF) relay device constituting a switch for an RF band.
2. Description of the Related Art
In a metering system for an RF band of several GHz such as a spectrum analyzer, a standard signal generator, and a network analyzer, a programmable attenuator is used as a means for varying an RF signal level. This programmable attenuator is constituted by a plurality of stages of the RF relay devices as described above. The performance, quality, and shape of the programmable attenuator are factors having a direct influence on the metering system. Most of the factors depend on the RF relay device as a component of the system.
FIG. 13 is a side view showing a conventional RF relay device disclosed as Published Unexamined Japanese Utility Model Application No. 63-69453.
Referring to FIG. 13, reference numerals 40 denote movable contact members; and 43, terminals. Each movable contact member 40 is brought into contact with a corresponding terminal 43 to electrically switch the circuit.
Reference numeral 41 denotes a shield for covering the movable contact members 40 and the terminals 43.
The above RF relay device, however, is of a one-transfer-type in which the central terminal 43 serves as a common terminal.
In addition, an electromagnet 2 for moving the movable contact members 40 must be arranged at the side of the shield 41 along a moving direction of the movable contact members 40. Therefore, an installation area of the entire RF relay device is undesirably increased.
Furthermore, since the movable contact members 40 and the terminals 43 are brought into direct contact with each other, contact surfaces are easily abraded after switching is performed a large number of times. In addition, since a contact resistance and the like are increased accordingly, RF characteristics are adversely affected, thereby degrading the durability of the relay device.
In addition the shield 41 is notched at the central portion of the longitudinal direction of the movable contact member 40, no isolation can be obtained.
FIG. 14 is an exploded perspective view showing a main part of another conventional RF relay device disclosed as Published Unexamined Japanese Utility Model Application No. 61-133943.
Referring to FIG. 14, reference numerals 401 and 411 denote movable contact members; and 341, 351, and 361 denote terminals fixed to a shielding case 331 by an insulating member 371. The movable contact members 401 and 411 are bought into contact with the terminals 341, 351, and 361 by a moving mechanism (not shown) to electrically switch the circuit.
The shielding case 331 covers the movable contact members 401 and 411 and the terminals 341, 351, and 361.
The shielding case 331 of the above RF relay device, however, is formed to cover the movable contact members 401 and 411 and the terminals 341, 351, and 361 in consideration of only external isolation. Therefore, since such an RF relay device is not particularly arranged in consideration of a characteristic impedance between the movable contact members, the terminals, and the shielding case, its usable frequency is at most 200 MHz. For this reason, this RF relay device cannot be used for a higher frequency band (1,000 MHz or more).
In addition, since no ground terminal is provided between the shielding case and each terminal, no isolation can be obtained.
Furthermore, if an electromagnet is arranged at the side of the shielding case in a horizontal plane, an installation area of the entire RF relay device is undesirably increased.
Note that the conventional RF relay device as shown in FIG. 13 or 14 is of a printed circuit board mounting type which can be mounted on a printed circuit board. However, a use frequency band of the above conventional RF relay device cannot reach an RF band of several GHz, and its reliability including reproducibility is poor.